Add binding documentation for the generic ARM SMC mailbox.
This is not describing hardware, but a firmware interface.
Signed-off-by: Andre Przywara <andre.przyw...@arm.com>
---
.../devicetree/bindings/mailbox/arm-smc.txt | 61 ++++++++++++++++++++++
1 file changed, 61 insertions(+)
create mode 100644 Documentation/devicetree/bindings/mailbox/arm-smc.txt
diff --git a/Documentation/devicetree/bindings/mailbox/arm-smc.txt
b/Documentation/devicetree/bindings/mailbox/arm-smc.txt
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+ARM SMC Mailbox Driver
+======================
+
+This mailbox uses the ARM smc (secure monitor call) instruction to
+trigger a mailbox-connected activity in firmware, executing on the very same
+core as the caller. By nature this operation is synchronous and this
+mailbox provides no way for asynchronous messages to be delivered the other
+way round, from firmware to the OS. However the value of r0/w0/x0 the firmware
+returns after the smc call is delivered as a received message to the
+mailbox framework, so a synchronous communication can be established.
+
+One use case of this mailbox is the SCP interface, which uses shared memory
+to transfer commands and parameters, and a mailbox to trigger a function
+call. This allows SoCs without a separate management processor (or
+when such a processor is not available or used) to use this standardized
+interface anyway.
+
+This binding describes no hardware, but establishes a firmware interface.
+The communication follows the ARM SMC calling convention[1].
+Any core which supports the SMC or HVC instruction can be used, as long as
+a firmware component running in EL3 or EL2 is handling these calls.
+
+Mailbox Device Node:
+====================
+
+Required properties:
+--------------------
+- compatible: Shall be "arm,smc-mbox"
+- #mbox-cells Shall be 1 - the index of the channel needed.
+- arm,smc-func-ids An array of 32-bit values specifying the function
+ IDs used by each mailbox channel. Those function IDs
+ follow the ARM SMC calling convention standard [1].
+ There is one identifier per channel and the number
+ of supported channels is determined by the length
+ of this array.
+
+Optional properties:
+--------------------
+- method: A string, either:
+ "hvc": if the driver shall use an HVC call, or
+ "smc": if the driver shall use an SMC call
+ If omitted, defaults to an SMC call.
+
+Example:
+--------
+
+ mailbox: smc_mbox {
+ #mbox-cells = <1>;
+ compatible = "arm,smc-mbox";
+ identifiers = <0x82000001>, <0x82000002>;
+ };
+
+ scpi {
+ compatible = "arm,scpi";
+ mboxes = <&mailbox 0>;
+ shmem = <&cpu_scp_shmem>;
+ };
+
+
+[1]
+http://infocenter.arm.com/help/index.jsp?topic=/com.arm.doc.den0028a/index.html
--
2.9.0
